Check that you have not left a non-bootable CD, diskette, or DVD in the drives of your PC, nor have any USB devices plugged in that the system might be looking to try to boot from.
If the above check is clear, then go into the BIOS settings and check that your internal hard disk drive is set as the first boot device or is ahead of any other disk drives you may have installed.
You cannot connect computers to each other by just using a standard USB cable - it doesn't work that way.
If you still cannot boot from your internal hard drive, then you should consider downloading a copy of Hiren's Boot CD
(which is a CD .ISO image) then burn this to a real CD and try booting from that media - you may have to select the CD as a boot device in your BIOS or if you get a boot options menu.
If you can boot the Hiren's CD ok, then your internal hard disk may have failed - you can test this with the DOS Programs of the Hiren's CD by selecting Hard Disk tools then selecting HDAT2 which will try to find any installed hard disks then allow you to test these and repair problems if possible.